The invention concerns a supercharged diesel engine with a Common-Rail injection system.
Common-Rail injection systems are increasingly used for better fuel efficiency and optimization of pollutant emissions of diesel engines. The system pressure obtainable in such fuel injection systems is very high. It does not depend on load and engine speed and allows optimal control of the injection process. In combination with an appropriate characterization of the charging, the result is an optimization of the combustion in all load ranges.
Besides the advantages described above, Common-Rail injection systems also have a disadvantage. The very high injection pressures that range from 1500 bar to 2000 bar today and will be even higher in future systems have to be controlled. This implies an extraordinarily high material stress, especially in areas of high fuel pressure such as the high-pressure fuel reservoir and the fuel injection lines of the injection system. In case of a breakage or leakage in such a high-pressure section of the injection system, fuel might leak out in the form of fine mist. To prevent ignition and hence explosive combustion, it is essential for leaking fuel to be collected safely and without reaching the surroundings, especially if engines with such injection systems are used in safety relevant locations.
In order to meet the mentioned safety requirements, it is known from DE 197 16 513 C2 to provide a casing for the fuel reservoir and the injection lines. The casing is realized in such a manner that the high-pressure fuel reservoir is integrated into a duct or channel, which is at least partly formed of the walls of the crankcase. This arrangement allows a safe casing of the endangered areas of the injection system, yet it has significant disadvantages in practical use. The crankcase has to be constructed a certain way if the casing is to be placed in it or next to it. Changes to the structure of the crankcase are a disadvantage, because it is a complex and very expensive component that often doesn't change throughout several engine generations or is used for various different engine types with different types of injection systems. Especially if a mass-produced engine was to be retrofitted with a casing, this would mean an expensive modification of the crankcase. In addition to that, the location of the crankcase is a highly unsuitable place for the high-pressure fuel reservoir because the large masses moved in the crankcase result in an increased vibration stress for the high-pressure fuel reservoir and the connected injection lines. Since the material stress is high anyway, increased vibration stress is to be avoided. Furthermore, the arrangement described above makes it complicated to collect, drain off and detect leaking fuel for there are different places where leaking fuel might accumulate.
Another fuel injection system is known from EP 0 690 221 A1. In this system, a high-pressure fuel reservoir supplied by a high-pressure fuel pump is integrated into the wall of a cylinder head cap of a diesel engine. Injection lines lead from the high-pressure fuel reservoir to fuel injection valves located in the cylinder head. This system is supposed to be advantageous because the high-pressure fuel reservoir is protected from vibration and damage. But placing the high-pressure fuel reservoir as described above has a significant disadvantage. Every time the cylinder head cap is demounted, which has to happen frequently for maintenance purposes, all connections from the high-pressure fuel reservoir to the fuel injection lines and to the high-pressure fuel pump have to be detached. Detaching of those sensitive connections, though, has to be avoided, both because screwing on and fastening of the fuel lines causes states of stress in them and because the system has to be kept extremely clean. Besides, a complete casing of the fuel injection lines is impossible because they have to be installed after the cylinder head cap has been mounted. Therefore, mounting openings are indispensable. Another disadvantage of the arrangement described above is that it cannot be used on individual cylinder heads, which are often part of diesel engines.
Another system known from DE 75 15 413 U1 shows an internal combustion engine on which all linesnecessary for fuel supply are placed in an extrusion, running parallel to one another. The extrusion can be integrated into an engine cowling or into a cooling air guidance means. Supposedly, the advantage of this arrangement lies in a grouping of the fuel lines that is easily understandable, safe to operate, easy to install and space saving. Meanwhile, it is a disadvantage that all fuel lines connected to the engine have to be detached when the engine cowling is demounted for maintenance purposes. Detaching of the fuel lines and especially of the high-pressure connections of Common-Rail injection systems has to be avoided for the reasons explained above. Besides, it is impossible to use this arrangement in combination with individual cylinder heads. Finally, an extrusion is not suited for a high-pressure fuel reservoir. The strength factors of such an extrusion are by far not enough regarding the pressures that need to be controlled.
Proceeding from this state of the art, it is an object of this invention to develop a diesel engine with a Common-Rail injection system in such manner, that the high-pressure section of the injection system is securely cased and well positioned concerning vibration. In addition to that, it is of importance that the position and casing of the high pressure reservoir and the fuel injection lines not require structural modifications of the crankcase or of the cylinder head and that the mounted casing not have negative effects on maintenance or repairing of the diesel engine.